I heard it can be very confusing for a first-timer if you don't know anyone there to show you the ropes.
Yes and no. It helps to have a group to camp with, as you'll probably have a better overall experience than camping in the "singles" areas. But otherwise, you can look at the schedules, find things to go watch or participate in, and go shopping.
The shopping is huge, BTW. We usually spend 2 days just doing that. It's all geared towards SCAdians and re-enactors, so it's not just the typical renfaire sort of shops, though there's a lot of cross-over.
I feel like Sca is that meet in the middle sort of medieval hobby. There is the Renfaire side of Medievalism(lol, I say that as if it were a religion) Then there is Sca, and then there is WMA, Re-enactments.
As far as larp goes, I am Highly Unfamiliar with it or the different kinds or where they fall into the mix.
Neither do I know where groups like the Order of the Marshall fall under nor how common they are.
Enlighten or correct me if I am wrong